The invention relates generally to electronic circuit board design, and more specifically to an enhanced plated-through hole design to facilitate high-performance and high-density connection.
Electronic circuits are typically constructed of electronic components that are mounted to a circuit board. The circuit board not only physically holds the electronic components, but also provides the electrical connections between the various components of the circuit. Because the circuit board therefore comprises a part of the circuit, its electrical characteristics must be considered in designing and laying out a circuit. Also, the desire to reduce the physical size of electronics devices must be considered in designing a circuit board, such that the electronic components and electrical connections between them take as little space as is possible.
Circuit boards found in modem electronic devices are typically boards that resemble a sandwich of insulating layers with conductors sandwiched in the space between. The conductors are often traces of copper that are relatively flat and therefore efficiently sandwiched in the space between insulating layers. The electrical components of the circuit are connected to the various traces sandwiched between or mounted on the insulating layers. Because the components can only be connected to metal pads on the circuit board, the circuit is constructed mainly by connection of components to metal pads on the exposed surfaces of the circuit board, and by interconnection of these component connections to circuit traces sandwiched between layers of the circuit board.
These connections between circuit board layers are often made by what is commonly known as a plated-through hole. A plated-through hole comprises a hole that extends through at least a portion of the circuit board, and between at least two layers of conductive traces. The hole is positioned between conductive traces on two or more layers of the circuit board, and is plated or coated with a conductive material. The conductive material electrically connects the conductive traces on the layers of the circuit board that the hole is positioned between, and forms a part of the circuit.
Plated-through holes therefore provide a way of connecting sandwiched layers of a circuit board to electronic components that are mounted to the exposed surfaces of a printed circuit board. Also, plated-through holes can provide connection to leaded electrical components whose leads or pins are placed into plated-through holes that extend through the circuit board. Although plated-through holes that extend to the surfaces of a circuit board can receive leads or pins of electrical components, the size of these plated-through holes is large relative to the electrical connector density of many modem surface-mount electrical components.
Plated-through holes that are used to provide electrical connection to surface mount components must further provide electronic contact pads on an exposed surface of the circuit board to which the electrical components can be connected. The plated-through holes are typically not routed to the surface of a circuit board in such circuit boards, but are connected to surface pads by a number of vias extending to another layer of the circuit board at which point they are connected to pads adjacent to the plated-through hole. Such circuit board construction takes space, from the plated-through hole layer to the surface layer, of whatever adjacent pads are necessary to provide connection to surface pads, and so takes a large area of the circuit board for a relatively small number of electrical connections. In addition to routing compactness, the inductance of such circuit boards is higher than is desirable, and other electrical characteristics such as resistance suffer. What is needed is a plated-through hole design that is more compact and has more favorable electrical characteristics such as inductance.
The present invention provides a circuit board with a plated-through hole, wherein a first end of the plated-through hole is electrically attached to a cap formed of conductive material. One or more surface pads terminate on a surface layer of the printed circuit board, and are connected to the cap by one or more vias extending from the cap to the one or more surface pads. In some embodiments, the circuit board is a substrate for mounting an integrated circuit, such as a ball-grid array integrated circuit.